Food processors have long felt the need for methods to prolong the shelf life of foodstuffs and/or increase microbiological stability of such foodstuffs. By increasing the amount of time a foodstuff is stable, processors can mitigate inventory losses due to spoiled foodstuffs. Prior methods, such as, the use of packaging, preservatives, and/or specific storage parameters (e.g., refrigeration) have been used to stave off spoilage.
Bacterial contamination of foods is known to be responsible for spoilage and for the transmission of food borne illness. In particular, Listeria monocytogenes has been associated with such foods as raw milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw meat sausages, raw and cooked poultry, raw meats (of all types), and raw and smoked fish. Listeria monocytogenes is a psychrotrophic food borne pathogen which is very widespread in the environment and in foods. The ability of Listeria monocytogenes to grow at temperatures as low as 3° C. permits multiplication in refrigerated foods.
Bacteriocins are antimicrobial peptides that are produced by bacteria and which have bactericidal action against closely related species. One of the most extensively characterized bacteriocin is nisin which is produced by a lactic acid type bacteria and which may be used to prevent growth of Gram-positive bacteria in a wide variety of different food products, particularly dairy products (see, e.g., U.S. Patent Publication No. 2008/0152757; U.S. Pat. Nos. 2,744,827; 4,584,199; 4,597,972; and 5,527,505).
Currently, most commercial refrigerated unaged, high moisture cheese products with relatively high pHs (e.g. above about 5.0) have a very limited shelf life and do not have secondary barriers to psychrotrophic pathogens. However, there have been efforts to enhance the microbiological safety of such cheese products. Generally, known methods to enhance microbiological safety in food products include cooking, adjusting water activity, adjusting pH, and/or using preservatives. However, these methods are generally expensive and therefore increase the cost of storing and producing the foodstuff while, in some cases, diminishing the organoleptic properties of the food product.